This invention relates to an exhaust system and particularly to an exhaust system for an internal combustion engine.

At present a range of mufflers are available for internal combustion engines. They are mainly incorporated as an aid to reducing noise pollution, while maintaining a desired back pressure on the engine to ensure optimum fuel throughput and efficiency.

In some conditions, for example, while racing, it is desirable to change the characteristics of a muffler to suit the modified engine operating requirements.

Presently exhaust flow is a compromise between a range of engine operating conditions, for example, noise emission, fuel economy and power output.

An object of the invention is to provide a muffler which overcomes the above identified problem.

A further object of the present invention is to provide an exhaust flow tailored to engine demand to provide a degree of control over noise emission and power output and to offer a consumer a useful alternative choice.

According to the invention there is provided a muffler for an internal combustion engine, the muffler including a casing in which a perforated or louvred baffle tube is mounted, the baffle tube having a shut-off valve therein so that the flow of exhaust gases can be directed straight through the baffle tube with the shut-off valve open or diverted through the perforations or louvres to increase the muffling effect and to

slow the flow of gases through the muffler when the shut-off valve is closed or partly closed.

The shut-off valve can be any flap valve, butterfly valve, vane or means for restricting the cross sectional area of the baffle tube.

The casing can be cylindrical, megaphone or any other suitable shape.

An area between the casing and the baffle tube can be packed with sound absorbing material and/or gas flow controlling material. The density of the material controls the amount of sound absorbtion and/or restriction to the gas flow. The area between the casing and the baffle tube can also be used for other flow or sound devices.

The baf le tube can be a through-pipe extending from an inlet to an outlet of the casing and can extend from the inlet part of the way to the outlet. Alternatively the baffle tube can extend from the outlet part of the way to the inlet.

The position of the shut-off valve can be controlled manually, mechanically or electronically.

Further aspects of the invention which should be considered in all its novel aspects will become apparent from the following descriptions which are given by way of example only.

Examples of the invention will now be described with reference to the accompanying drawings in which:

Figure 1 shows a diagrammatic section through an example of the muffler according to the invention;

Figure 2 is a diagrammatic section of an inlet region of the muffler shown in Figure 1;

Figure 3 is a diagrammatic sectio ^' of a shut-off valve assembly for the muffler shown in Figures 1 and 2; and

Figure 4 is a diagrammatic section through an example of the muffler according to the invention with an adjustable shut- off valve operable from a position remote from the muffler.

The muffler 1 shown in Figure 1 has an inlet connecting tube 2 the end of which 3 is adapted for connection to an outlet tube (not shown) of an internal combustion engine. The other end of the connecting tube 2 is connected to one end of a casing or body 4 of the muffler 1. An outlet tube 5 is connected to the other end of the casing or body 4.

The casing or body 4 has a baffle tube 6 mounted therein. Alternatively (not shown) the baffle tube 6 can extend only part of the length of the connecting tube 2 towards the outlet tube 5, for example about half to three quarters of the length of the casing or body 4.

The baffle tube 6 is perforated or louvred 7 along at least part of its length. The baffle tube 6 has mounted therein a shut-off valve 8 which is part of an adjustable valve assembly 15 illustrated in Figure 3. The valve assembly 15 can be mounted at any position along the baffle tube 6.

In Figure 2 is shown an inlet connecting tube 2 welded to an end cap 10. The flared end 14 is attached to the perforated or louvred baffle tube 6. The end 14 can optionally be straight or tapered. The baffle tube 6 can be mounted

concentric with or offset from the centre of the casing or body 4. The end cap 10 is attached by suitable means to the inlet connecting tube 2 to secure it in place.

The adjustable valve assembly 15 illustrated in Figure 3 comprises a valve which in the example illustrated is a butterfly valve 8. This butterfly valve is secured to a hollow shaft 9 which is inserted into holes drilled through the baffle tube 6. From the end 11 of the hollow shaft 9 projects a grub screw 16. A nut 13 is fitted on the grub screw 16 and is secured to the shaft 9 and the grub screw 16 by welds or other means. To lock the valve 8 in position a lock nut 12 is screwed down the grub screw 16 and tightened, pinching the casing 4 between the nut 13 and the lock nut 12 to create a relatively gas-tight seal.

To move the valve 8 from its open position to its closed position an Allen key is inserted in the grub screw 16 to turn the shaft 9.

The valve is mounted directly into the baffle tube or optionally into a sleeve 17 fitted to the baffle tube 6.

In use the position of the valve relative to the baffle tube 6 can be adjusted manually, mechanically or electronically by means (not shown) to enable the valve to be moved from a closed position to an open position or to any intermediate position.

In its closed position the flow of exhaust gases is in the direction of arrow 18 through the perforations at the inlet end of the casing 4 and to an annular space 20, formed between the

baffle tube and the casing before the gases re-enter the baffle tube 6 and pass from the outlet 5.

The annular space 20 can be packed with sound absorbing and/or flow controlling material in such quantities and combinations as are necessary to optimize noise reduction and flow control for the type of engine onto which the muffler is to be fitted.

In its open position the back pressure at the exhaust manifold is reduced and the flow of gases is directed through the baffle tube and past the valve.

Figure 4 illustrates a diagrammatic section illustrating a remotely controlled shut-off valve.

In this example the valve 8 is able to be controlled remotely from the muffler 1. One end of the hollow shaft 9 is attached to a lever 19 which is connected to suitable control means (not shown) which enables the valve to be opened or closed to suit a user's requirements and the type of engine to which the muffler is to be fitted. Alternatively an automatic control from the engine to the muffler may be used to vary the flow of exhaust gases according to the needs of the engine. It is envisaged that a computer and/or electrical circuit will eventually control the movement of the valve.

The muffler can be constructed having a variety of lengths and taper angles to suit the characteristics of the engine to which the muffler is to be fitted.

Thus by this invention there is provided a muffler for an internal combustion engine.

Particular examples of this invention have been described and it is envisaged that improvements and modifications can take place without departing from the scope of the appended claims.